(1) Field of the Invention
This invention relates to an inverter unit, an integrated circuit chip, and a vehicle drive apparatus and, more particularly, to an inverter unit for controlling an AC motor, an integrated circuit chip for driving an inverter circuit including a plurality of high breakdown voltage semiconductor elements, and a vehicle drive apparatus for driving vehicular tires by an AC motor.
(2) Description of the Related Art
In recent years attention has been riveted on environmental problems, such as emissions of carbonic acid gas which cause global warming and air pollution. Hybrid electric vehicles (HEVs) in which a conventional internal combustion engine and electric drive by a motor are combined have occupied attention because they can not only reduce harmful substances included in their emissions but also improve fuel efficiency.
One of key parts included in an HEV is an inverter unit which enables the electrification of a drive system.
FIG. 7 shows an inverter unit used in a conventional HEV.
An inverter unit 800 for conventional HEVs comprises a microcontroller unit (MCU) 810, a pre-drive unit (PDU) 820, a protection and insulation circuit 830, a three-phase inverter circuit 840, and a smoothing capacitor 850 (see, for example, Mitsubishi Electric Corp. Technical Reports, vol. 74, No. 9, 2000, pp. 31-34 (FIG. 4)).
The MCU 810 receives a motion control signal (not shown) for the HEV or a signal from a sensor 901 which detects the number of revolutions and the like of an AC motor 900, and outputs an inverter control signal to the PDU 820.
The PDU 820 is a circuit section for driving and controlling the three-phase inverter circuit 840. The PDU 820 receives the signal from the MCU 810 and operates.
The protection and insulation circuit 830 protects the PDU 820 and the three-phase inverter circuit 840 and insulates them. The protection and insulation circuit 830 includes a sensor for detecting an abnormality. The protection and insulation circuit 830 prevents noise which occurs due to, for example, the malfunction of the three-phase inverter circuit 840 from flowing into the PDU 820.
The three-phase inverter circuit 840 includes six insulated gate bipolar transistors (IGBTs) 841 and six fly wheel diodes (FwDis)) 842. Each IGBT 841 and each FwDi 842 are connected in parallel. Three combinations of two IGBTs 841 and two FwDis 842 form the three-phase inverter circuit 840. The breakdown voltages of the IGBTs 841 and the FwDis 842 are 600V, so they can withstand a battery voltage of 350V supplied by power supply 902.
In the inverter unit 800 having the above structure, the three-phase inverter circuit 840 controls the three-phase AC motor 900 which drives vehicular tires (not shown). One three-phase AC motor 900 is mounted in one vehicle and is fixed to a shaft which connects two tires.
FIG. 8 shows the detailed structure of the PDU included in the inverter unit used in the conventional HEV. This circuit is indicated in, for example, the above-mentioned Mitsubishi Electric Corp. Technical Report.
The PDU 820 is a circuit section for controlling the switching of the IGBTs 841 included in the inverter circuit 840. Basically, the PDU 820 is divided into a circuit section for controlling operating timing of the IGBTs 841 and circuit sections for outputting a drive signal for driving the IGBT 841 according to the timing. A central processing unit (CPU) 821, being an IC, corresponds to the circuit section for controlling the operating timing of the IGBTs 841. Very large scale integrated circuits (VLSIs) 822 correspond to the circuit sections for outputting a drive signal (hereinafter also referred to as a gate signal) to the IGBT 841. One of these circuit sections is necessary to each IGBT 841.
The PDU 820 also includes photocouplers (indicated by “Isolation-IC” in FIG. 8) 823-1 through 823-11 for transmitting signals between the circuit sections or for ensuring safe operation by preventing noise from being mixed into a signal inputted from or outputted to the MCU 810, a low-pass filter 824 for cutting off high frequency components of a signal inputted from the MCU 810, a converter 825 for converting a signal outputted from the CPU 821 into a DC signal and for outputting it to the MCU 810, a DC/DC converter 826, and buffers 827 each located between the VLSI 822 and the IGBT 841 as discrete components which are not incorporated into an IC.
Only circuits for driving one phase of the inverter are shown in FIG. 8, but circuits for driving and controlling the three phases of the inverter are included in the real PDU 820.
When an abnormality occurred in the IGBT 841, the operation of the inverter circuit 840 must be stopped. Accordingly, temperature detection results obtained by temperature sensors 831 and electric current detection results obtained by current sensors 832 are fed back to the PDU 820 to control the outputting of drive signals. This circuit function corresponds to the protection and insulation circuit 830 shown in FIG. 7. The operating timing of the IGBTs 841 is controlled by a signal outputted from the MCU 810. An electric current detection result, a rotational speed detection result, and a temperature detection result obtained from the AC motor 900 by a current sensor 901a, a rotational speed sensor 901b, and a temperature sensor 901c, respectively, are fed back to the MCU 810.
Characteristics of the above conventional PDU are (1) that it is a hybrid IC including the ICs and the discrete components, (2) that the control circuit section for controlling the timing of the IGBTs 841 and the circuit sections for outputting a gate signal to each IGBT 841 differ from one another in reference potential, that is to say, there are five or more reference potentials, and (3) that signals are transmitted between the circuit sections via the photocouplers and signals are inputted from or outputted to the outside via the photocouplers.
With the inverter unit to be mounted in a vehicle, protection against noise is important. It is necessary to prevent noise produced by the switching of the inverter circuit from flowing into the PDU or the MCU. Therefore, the above characteristics (2) and (3) are necessary to the PDU.
To promote the spread of the HEV system, at present there are strong demands for compact, light, low-cost high performance inverter units for use in HEVs. In addition, high reliability and high cooling performance are required.
However, conventional PDUs are hybrid ICs. One hybrid IC includes various ICs and elements are necessary for protecting these ICs. Therefore, a large number of parts are used in one PDU. This increases the area of a PDU section, resulting in the difficulty of miniaturizing an inverter unit or making it lighter.
In addition, with conventional PDUs, signals are transmitted between circuit sections via photocouplers and signals are inputted from or outputted to the outside via photocouplers. However, the reliability of these photocouplers is low at high temperatures. To ensure the reliability of conventional PDUs at high temperatures, cooling systems are necessary. This is also a barrier to miniaturization. Furthermore, about fifteen photocouplers are used in one conventional PDU, resulting in the high costs of an inverter unit.
To solve these problems, a method for realizing miniaturization by forming a PDU as an integrated circuit is disclosed (see, for example, Japanese Unexamined Patent Publication No. 2004-120917 or No. Hei 5-316755 (FIG. 6)).
Furthermore, an interface circuit which is included in an IGBT control unit for driving a motor and which replaces the photocouplers is disclosed as a technique for eliminating the photocouplers (see, for example, Japanese Unexamined Patent Publication No. 2004-173413).
With the PDU disclosed in, for example, the Japanese Unexamined Patent Publication No. 2004-120917, however, a circuit section for driving and controlling IGBTs for driving a motor is formed as multiple chips. Accordingly, there is a limit to the miniaturization of the PDU.
In the Japanese Unexamined Patent Publication No. Hei 5-316755, a power supply is shared by a circuit section for outputting gate signals to IGBTs on the lower arm side (low voltage arm side) and a circuit section for controlling the operating timing of the IGBTs. Accordingly, this method cannot prevent noise from flowing into the PDU via a power supply system. The reliability of a PDU made by this method deteriorates.
In the Japanese Unexamined Patent Publication No. 2004-173413, the interface circuit which replaces the photocouplers is disclosed, but integration of a PDU or making reference potentials independent of one another is not disclosed.